Effect Of Nitrogen And Drought Stress On Growth And Expression Of Genes Encoding Nitrogen Absorption And Assimilation At Winter Wheat Seedling Stage

Nitrogen and water are the two important essential for nutrient absorption production of wheat. Insufficient N severely affects the yield of crops worldwide, application of Nitrogen fertilizer could significantly increase crop yield, however N use efficiency(NUE) is often low, lead to serious environmental pollution. Water deficits are often associated with reducing in N availability. In practice, the combination of nitrogen and drought stresses appeared at the same time. Therefore, we simulated water stress using the polyethylene glycol(PEG)- 6000, two different wheat genotypes, Yumai49-198 and Zhoumai22, were grown in Hoagland’s nutrient solution. The objective of this study was to understand the wheat seedling growth and the physiological and molecular responses about nitrogen absorption and assimilation under different nitrate and water supply at seedling stage. The main results are as follows:1. N stress、drought stress and the combination of stress(N0+PEG) significantly inhibited the growth of wheat seedlings, but promoted the growth of root. The data show that N and drought stress for 5 days significantly decreased the size of the leaf, plant height, shoot dry weight of stems and leaves; N stress significantly increased the root length, root fresh and dry weight and root shoot ratio; drought stress significantly increased the root dry weight and root shoot ratio. The combination of stress(N0+PEG) had largest influence on phenotype traits in wheat seedling.2. N stress significantly reduced the wheat seedlings chlorophyll a and chlorophyll b, total chlorophyll and carotenoid content, as well as total nitrogen、nitrate、soluble protein and free amino acid content, GS activity and NR activity of leaf, drought stress significantly decreased total nitrogen、nitrate content, NR activity of leaf, but the decline was less than that under N stress. Drought stress significantly increased chlorophyll a and chlorophyll b, total chlorophyll and carotenoid content and osmotic regulation substances soluble protein and free amino acid content, and the increase of free amino acids is greater than soluble protein. Under water stress, the activity of GS in leaves was differentially between the two genotypes: significantly increased in Yumai48-198, while, decreased in Zhoumai22.3. Expression profiles of these nitrate transportation protein genes Ta NRT1 and Ta NRT2 were determined by quantitative real-time polymerase chain reaction(q PCR) analysis after 5 days N stress and drought stress. The transcription levels of Ta NRT1.1 and Ta NRT1.2 were up regulated under N stress, down regulated under drought stresses, it seems that nitrogen stress induced Ta NRT1.1 and Ta NRT1.2 expression plays an important role in the process of nitrogen absorption, in order to promote the absorption of N. vxczThe transcription levels of Ta NRT2.1、Ta NRT2.2 and Ta NRT2.3 were significantly decreased under N stress and drought stresses, However, no significant difference was found between PEG and N0+PEG treatment in both cultivar. We suggest that the significant decrease expression of Ta NRT2 under combination stress was might due to the drought.In conclusion, compared with the control(N), the Ta NRT1.1 and Ta NRT1.2 were higher expressed after 5 days different stresses than Ta NRT2.1、Ta NRT2.2 and Ta NRT2.3, thus, we suggest that the Ta NRT1.1 and Ta NRT1.2 may play more important role in nitrate absorption and transportation after 5 days N stress and drought stress.4. Expression profiles of the genes Ta GS1 and Ta GS2 were determined by q PCR. Ta GS1 and Ta GS2 were up-regulated after 5 days N stress in winter wheat seedlings, drought stress for 5 days, the expression of Ta GS1 and Ta GS2 in leaves had significant genotype differences: in Yumai49-198 down-regulated, in Zhoumai22 up-regulated. Compare the GS activity with Ta GS1 and Ta GS2 gene expression, under water stress, the expression of Ta GS and GS activity in wheat seedlings is not only affected by nitrogen nutrition regulation, but also related to genotypes. In addition, Ta GS1 and Ta GS2 expression and GS activity showed different changing trend, which suggest that nitrogen assimilation is a complex regulatory mechanism of wheat and remains to be further researched.